Spatial coherence is a fundamental property of light that contains spatial information, and is therefore of great importance in applied and basic science. Here we present an efficient method for controlling the spatial coherence of a modified degenerate cavity laser, with little variation in output power. By introducing loss to certain modes and utilizing mode competition, the number of lasing modes is varied over five orders of magnitude, while the total output power decreases by less than a factor of three. Furthermore, the number of lasing modes supported by the cavity can be fully controlled in one dimension, while left unaltered in the other. We also show that our method can produce interesting spatial coherence functions, such as a cosine or Bessel functions.